Thunbergia alata: Black-eyed Susan
Thunbergias may be said to be still waiting to be ‘discovered’. The species is one of the few that are found in cultivation even though it cannot be said to be the prettiest of the 100 or so known species that make up the genus. Nevertheless, it is a nice plant and suitable for growing as a house plant.
Black-eyed Susan is generally grown as an annual sown in March. In a sunny, sheltered spot in the garden it will flower from June until autumn, but it does better indoors where it should be put in full sun. The growing medium should be fairly heavy, such as John Innes potting compost No. 2. Water should not be supplied too copiously even in summer and should be practically withheld in winter, when the plants are moved to an unheated room. They quickly make new growth after springwhen provided with warm conditions, and soon bear – after about Vh months.
The type species has flowers about 2.5 cm (1 in) across, but in some cultivars they are twice as large. It is interesting to note that the species primarily grown in cultivation are from Africa, be it T. natalensis, T. erecta or T. gibsonii.
Much prettier thunbergias, however, may be found in the tropical regions of Asia, even though most are quite large climbers. Nevertheless, their blooms, which often measure up to 10 cm (4 in) across and are borne in pendant, many-flowered clusters, fully make up for the space they occupy. T. grandiflora from northern India has lovely pale blue flowers almost 8 cm (3 in) across, in long, thick clusters; T. laurifolia from northern India and Malaysia has lavender-blue flowers with a creamy throat; T. coccinea (syn. Hexacentris coccinea) from India and Burma, with 50-cm-(20-in-) long clusters of scarlet flowers only about 1.5 cm (¾ in) across, is one of the loveliest members of the genus; and T. fragrans, from the same area, is the recommended choice for those who like white flowers. Cultivation is the same as for the species, but the winter rest period is not as pronounced.